Automatic arc-started thermochemical metal removal apparatus



July 4, 1950 oaosco 2,513,425

AUTOMATIC C-STARTED THERMOCHEMICAL MET REMOVAL APPARATUS Filed Jan.24, 1945 INVENTOR ROSCOE R. LOBOSCO ATTORN EY Patented 'July :4, 1950 AUTOMATIC ARC-STARTED THERMOCHEM- ICAL METAL REMOVAL APPARATUS Roscoe R; Lobosco, Elizabeth, N. J;, assignor' to The Linde-Air Products Company, a corpora,- tion of Ohio Application January 24, 1945, Serial No. 574,432

6 Claims. 1,

This invention relates to the art of working metal by directing preheating flame and a stream of oxidizing gas onto a metal body, and more particularly to auxiliary electrically energized heating to start the operation.

In certain processes such as the oxygen deseaming or cutting of ferrous and non-ferrous ma terials, it is usually necessary to initially preheat the work to a temperature of approximately 1600" F. in order to start the process and to supply further preheat while the process is being carried out. This preheat is usually supplied by oXy-acetylene flames, although other fuel gases such as propane and city gas, are sometimesused. The time required for the initial preheat is nonproductive and often represents a large partof the total time required for the entire process. Therefore, any means of reducing or eliminating the tim formerly required by the initial preheat period would. result in a substantial saving in both time and production cost.

In thermochemically removing metal from a ferrous metal body with an oxygen stream, there is now coming into vogue what is known as the post-mixed or externally mixed oxy-fuel gas flame for preheating the work for starting and carrying on the operation. In. such flame the oxygen and fuel gas are combined or mixed outside of the nozzle means so that flashback and backfire are avoided. The latter are very objectionable incidents to'a high combustible mixture of oxygen and fuel gas in a common passage which leads to the nozzle discharge orifice for maintaining a premixedoxyduel gas flame. The post-mixed flame, however, is not as hot as: the premixed flame, and is better suited for preheating hot work than cold work.

To overcome the difficulty of initially starting an oxygen cutting operation with post-mixed preheating flames, it has been proposed to use premixed flames for initially heating the work, but the latter type of flames are subject to flashback and backfire. Hence, there exists a need for some auxiliary heating means for initially starting a metal removal operation, especially on cold work where such metal removal operation involves the use of post-mixed preheating flames. Such need is more acute where the operation must be initiated on the surface of a metal body at a spot which is spaced from. the

edges of such surface, due to the greater heat conductivity from such spot. This applies to cutting as well as to deseaming.

An object of this invention is to reduce the initial starting time of the operation while over.-

coming difficulties and disadvantages of the prior art. Other important objects are to provide improved methods and' means for thermochemically working metal bodies.

In accordance with the invention a metal removal operation is very quickly started electrically by heating only a local surface portion or small zone on the work, the electrical heating being discontinued when the temperature of such portion is raised to a value sufiicient for thermochemical reaction of the heated metal with the oxidizing gas stream and oxy-fuel preheating flame employed in; such metal removal operation. Alternating ordirect current or both may be used. Electrical arc, resistance, or induction heating may be used separately or in combination. If an electrode is employed, it be composed of refractory or non-refractory material. The current, if alternating, may be high or low frequency or both. Adjuvant material or powder may also be used in the starting zone to decrease the starting'time. So called flying starts are made-possible by the invention.

In carrying out the invention, using a hand deseaming blowpipe and a carbon on cold Work, the. deseaming operation was started in less than second after the arc was struck. The normal preheat time without the arc is about 30 seconds.

Referring to the drawings:

Fig; 1 is a view mainly in side elevation of deseaming or desurfacing apparatu exemplifying one form" of the invention;

Fig. 2 is a similar view of another form of the invention; and

Fig. 3 is a fragmentary sectional View showing the internal structure of a nozzle.

InFig. 1- abody B, composed of ferrous metal such as steel for example, is supported on a conveyor: roll table T under a desurfacer D. The desurfacer D includes a row of inclined water cooled nozzles N which are to discharge streams of commercially pure oxygen preheating-flame gases composed of oxygen and fuel gas such as acetylene at an'acute angle onto the top surface of the body B. The nozzles N supplied with cutting oxygen by suitable means including'a supply pipe 0 containing a valve V0, and with acetylene gas by suitable means including a supply pipe A including a veil Va. The valves. Va and V0 are controlled by means comprisingsolenoids Sc and So which are, in turn, operated by a timer ii. The timer ifl also operates a solenoid Se which controls a valve Ve in a pneumatic or hydraulic supply pipe H. The

B. A screw 2!) normally supports the link L so 1 that the gaps between the electrodes and the work may be readily adjusted. 1

The timer I controls the electrical energy supplied to the electrodes E and the body B through suitable circuits including an inductive coupling I and a reactance Z. A suitable source of alternating current AC is connected to the timer Ill.

, In operation, the timer l0 energizes circuit 22 and establishes an electric arc X between each electrode E and the adjacent spot of surface metal on the body B in line with a cutting oxygen orifice. Such arc X rapidly heats the metal at such spot to the ignition temperature. The timer H! thereupon deenergizes the circuit 22 and energizes circuit 2d which results in the elevation of the link L and all of the electrodes E, moving the lower ends of the latter out of the reaction zone. At the same instant, circuits 26 and 28 are energized by the timer l0, resulting in oxygen and fuel gas being supplied to the nozzles N, and the roll table T is operated to advance the body B toward the right, so that thermochemical deseaming or desurfacing is accomplished.

The arcing zones may be covered with ferrous metal powder P, as shown in Fig. 2, at the start of the electrical heating period, if desired, and the current may be direct. In thiscase, the polarity of the work B is preferably positive and the electrode negative, because of the greater heat input, and because a more stable arc is obtained. The ferrous metal powder P facilitates the establishment of the arc and leaves a deposit of molten metal on the work which is highly reactive with the cutting oxygen stream, insuring a positive and very quick start.

Another method which can be used according to the invention is to attach the electrode to a cutting blowpipe in the line of cut and a little ahead of the nozzle. Such method is particularly suitable for machine cutting if an automatic means, such as superimposed high voltage, is used to establish the arc. The machine couldthen be run toward the work, the are established, and the cut picked up without any lost time for preheating.

Either a carbon or a metallic electrode can be used. Where a carbon electrode is used, the resultant hot spot of metal on the work starts the operation. Where a metallic electrode is used, the resultant small puddle of molten electrode metal which is quickly produced, starts the process. If the spot on the work beneath the elec trode is covered with metallic powder, or if a slug of powder is blown into the arc, a number of molten droplets of metal will be obtained which provide quick starting for the deseaming proc-'- ess. Once the process is started, the arc can be stopped, but it may be continued if desired. However, in many case the continuation of the are beyond the initial preheat period may produce undesirable results. For example, if the arc is maintained after the initial preheat in shape cutting, there is a tendency to produce a more ragged out than can be obtained with gas preheat alone.- 1

Where direct current is used, it is generally better, as pointed out above, to have the polarity 'of the work positive because of the greater electrical heat input to the work and because a more stable arc is obtained. Coated electrodes can be used where they are metallic. In order to reduce the preheat time as much as possible, current densities greater than those generally used in arc welding can be used since the preheat time is very small and occurs at comparatively widely spaced intervals. For this reason, a power supply having a short time rating can be employed, thus reducing the cost and size of the apparatus.

I The are may be struck in the conventional manner by touching the work and then retracting the electrode a short distance. This can be done by manual. or automatic means. The electrode may be spaced a proper distance from the work and the are established by bridgin the gap with a super-imposed high voltage of high frequency. Starting material such as steel wool may be inserted between the electrode and the work to start the arc. The use of metallic powder to bridge the gap between the electrode and the work, establishes the arc very quickly and results in a puddle of molten metal. If the electrode rests very lightly on the work and electrical current is passed through the electrode and the work, the poor contact thus established results in arcing between the electrode and the work and in a hot spot on the work. While the latter is not as rapid as the other methods, the system is very simple.

Either the arc itself or the hot spot left by the arc on the work can be used to ignite the preheat gases.

The manner in which the starting electric preheat apparatus is combined with the blowpipe apparatus depends on each particular application. In the case of machine deseaming, it is desirable to remove the electrode and any associated apparatus out of the oxygen stream as soon'as the work is electrically heated to the desired temperature. This may be done by any suitable means. In certain cutting applications where the starting electrode is not in the oxygen stream, the electrode need not be removed from its normal position.

Iclaim:

1. Apparatus for performing a metal-removing operation such as desurfacing or deseaming a metal body, comprising, in combination, nozzle means for discharging oxy-fuel gas flame and an oxidizing gas stream onto said body, means positioning an electrode with one end in stationary position with respect to the surface of such body, means including such electrode for electrically heating a local portion of said surface for combustion with such oxidizing gas stream, and automaticmeans operative to remove the end of said electrode from such stationary position and out of y the flame and oxidizing gas stream immediately after the local surface portion of such body has been so heated; said automatic means comprising a circuit including the electrode and body, and an electrode elevator. I 2. Apparatus as defined by claim 1, in which the means for electrically heating the local surface portion of the ferrous metal body comprises means for forming an electric current between said electrode and such surface portion, and the electrode is composed of ferrous metal, so that molten ferrous metal from the end of the electrode deposited upon thebody.

3. Apparatus as defined by claim 1, in which the electrical heating means comprises means for forming an electric arc between the end of such electrode and the body.

4. Apparatus as defined by claim 1, which includes an automatic timer for operating the several means including said automatic means in proper timing relation to perform the metal removing operation and remove the electrode from the metal-removing reaction zone as soon as the metal-removing operation starts.

5. In a desurfacing machine, the combination with means for producing a preheating flame and a desurfacing stream of oxygen, of automatic means for electrically preheating the work to start the desurfacing operation, comprising an electrode, means supporting said electrode for movement with respect to the work, an electric circuit including such work and the electrode for forming an electric are between said electrode and the work in the zone where said stream of oxygen impinges against the surface of such Work, means for energizing said circuit to form such are, means for moving said electrode with respect to the work, and automatic means for operating said circuit energizing mean-s and said electrode moving means so that the resulting arc in such zone causes the desurfacing operation to start and the electrode to be removed from the desurfacing reaction zone as soon as such operation starts.

6. Apparatus for automatically starting the reaction of a thermochemical metal removal operation involving heat and a stream of oxidizing gas applied to a metal body, comprisin an electrode holder for positioning an electrode with its end located adjacent the body in line with such stream of oxidizing gas, an electric circuit including the body and said electrode adapted when energized to ignite metal between the end of said electrode and the body to quiclny start the metal removal operation of such stream, and means including a timer operative to elevate said electrode holder when the reaction starts.

ROSCOE R. LOBOSCO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 866,498 Menne et a1 Sept. 17, 1907 968,350 Harrison Aug. 23, 1910 999,099 Debus et a1 July 25, 1911 1,137,834 Bowers May 4, 1915 1,494,003 Malcher May 13, 1924 1,585,893 Coberly May 25, 1926 1,709,886 Smith et al. Apr. 23, 1929 2,110,781 Wagner Mar. 8, 1938 2,210,403 Skinner Aug. 6, 1940 2,278,569 Shrubsall Apr. 7, 1942 2,286,192 Aitchison June 16, 1942 2,288,027 Scheller June 20, 1942 2,289,968 Jones July 14, 1942 2,309,096 Bucknam et al. Jan. 26, 1943 2,381,355 Laughton, Jr Aug. 7, 1945 FOREIGN PATENTS Number Country Date 552,321 Great Britain Apr. 1, 1943 641 Australia Feb. 19, 1926 OTHER REFERENCES Engineering and Mining Journal, November 9, 1901, page 604. 

